Settings in 'cm' units


I’ve checked the differences between several settings for units.

Now I want to use ‘cm’ units only because I want to make sure that the position of stimulus is absolute rather than relative to the screen and I know that the physical monitor dimensions will be required if I use ‘cm’ units. It seems that the physical size including the width and the height of the screen as well as the resolution are the information required to get the ‘cm’ units correct.

PS: I use coder and the experiments will be local, not online.

What is exactly I should do if I want to assure the stimulus is presented in ‘cm’ units? In builder we are instructed to ask monitor center for “help”. But in coder, do I need to make sure that everything is organized in ‘cm’ units? For example:


Do I need to make sure that the units I use are kept the same as ‘cm’ units everytime I need to?

How should I input the specific parameters if I should complete monitor setting?

Suggestions in Building experiments in psychopy is that I can measure the actual physical size of screen by a tape. It seems that it’s not accurate enough. Is there problem if there exists some error here?